In general, unlike primary batteries that are not chargeable, secondary batteries denote batteries that are chargeable and dischargeable. Secondary batteries are being widely used in high-tech electronic devices such as cellular phones, notebook, computers, camcorders, and the like. Particularly, lithium secondary batteries, which have an operating voltage of 3.6 V, are being actively developed. This is because the operating voltage of the lithium secondary batteries is approximately three times higher than that of nickel-cadmium batteries or nickel-hydride batteries, which are widely used power sources for electronic devices and because the lithium secondary batteries have excellent energy density per unit weight.
Such a lithium secondary battery generally employs a lithium-based oxide as a cathode active material and a carbon material as an anode active material. In general, the lithium secondary batteries are classified into liquid electrolyte batteries and polymer electrolyte batteries. Batteries using a liquid electrolyte are referred to as lithium-ion batteries, and batteries using a polymer electrolyte are referred to as lithium-polymer batteries. Also, the lithium secondary batteries are manufactured in various shapes such as cylindrical, prismatic, and pouch shapes.
FIGS. 1 to 4 are views of an upper insulator of a secondary battery according to the related art.
As illustrated in FIGS. 1 and 2, a secondary battery according to a first embodiment of the related art includes a can, an electrode assembly accommodated in the can and constituted by a cathode tab, a separator, and an anode tab, a cap plate coupled to an opened upper end of the can to seal the upper end of the can, and an upper insulator 10 disposed under the cap plate and having a hole passing through the cathode tab and the anode tab.
Here, the upper insulator 10 has a prismatic shape. Also, the upper insulator 10 has an anode tab hole 11 for the anode tab, an injection/impregnation hole 12 for injecting and impregnating, and a cathode tab hole 13 for the cathode tab in an upper portion thereof.
However, in the upper insulator 10 of the secondary battery according to the first embodiment of the related art, the anode tab hole 11, the cathode tab hole 13, and the injection/impregnation hole 12 are eccentrically formed. Thus, stress may be concentrated into a portion having relatively low resistance against the external force to cause defects in the upper insulator. Furthermore, if the upper insulator 10 is misaligned in front and rear or left and right directions, it may be difficult to assemble the upper insulator 10. As a result, it is cumbersome to assembly the upper insulator 10 in a state where the upper insulator 10 is aligned in the same direction.
Thus, as illustrated in FIGS. 3 and 4, an upper insulator 10 of a secondary battery according to a second embodiment of the related art has an injection/impregnation hole 12 and an anode tab hole 11, which have the same size, to improve assemblability and bending resistance. However, since the injection/impregnation hole 12 is narrow in space and deteriorated in workability, and also, the cathode tab hole 13 is eccentrically formed, the assemblability may be deteriorated, like the first embodiment.